1. Field of the Invention
The present invention relates generally to multimedia transmission systems and more particularly to systems and methods for transmitting high definition digital video and standard definition analog video over a single cable.
2. Description of Related Art
With the advent of digital broadcast television and streaming video technologies various video cameras, monitors and video recorders have become available with enhanced resolution and advanced features. Closed circuit television (CCTV) systems now offer high definition video outputs and compressed digital video signals for use in applications such as premises surveillance, access control and remote monitoring of facilities. However, legacy systems remain in place and standard definition analog video signals are in widespread use and will continue to be used during the transition to all-digital, high-definition systems. In particular, coaxial cable (coax) has been extensively deployed to carry signals from analog CCTV cameras to monitoring stations. Also, some deployed CCTV cameras transmit compressed digital video signals over local area networks, and these cameras may use the Internet Protocol (IP) as a communications means for transmitting the compressed video signal over category 5 (CAT5) twisted pair cable.
FIG. 1 illustrates a system using coax to carry standard definition analog video. A basic analog camera typically generates a composite video baseband signal (CVBS) that can be transmitted up to 300 meters or more using Coax. The CVBS signal is commonly provided to a video recording system which often comprises a digital video recorder (DVR) that digitizes the CVBS signal and records it. A conventional monitor or display device may be connected directly to the coax to display live standard definition video and to the DVR for playback of recorded video. The standard definition (SD) video typically has a resolution of 720×480 pixels.
FIG. 2 illustrates approaches to transmitting high definition (HD) video (1920×1080 pixels) in currently deployed systems. An IP based, HD camera may generate a compressed digital HD video signal over 100 Mbps Ethernet using standard CAT5 twisted pair cable for distances up to 100 meters. The signal is received by a host processor and DVR. The HD video can be viewed live and also recorded for non-real time playback. The use of IP networking to enable the camera to transmit digital video allows these systems to add some upstream communications from the monitor (display) side back to the camera side, typically camera control and audio signals. It should be noted that for the live video, noticeable delay may occur due to latency in the IP network and due to the time needed for the host processor to reconstruct the compressed digital video. However, the use of IP networking enables the use of networking tools, including routers, to combining traffic to or from multiple cameras and/or DVR recording and monitoring devices in different network connected locations.